As described in, for example, Patent Publication 1, an intake system for an internal combustion engine normally includes an air cleaner to capture foreign material such as dust that is suspended in the intake air. The air cleaner includes a housing, the interior of which is partitioned into a pre-filtering chamber and a post-filtering chamber by a filter. The pre-filtering chamber includes an inlet port. Atmospheric gas, namely, air, is drawn into the pre-filtering chamber through the inlet port. The air drawn into the pre-filtering chamber is drawn into the post-filtering chamber through the filter. As the air passes through the filter, the filter captures foreign particles that are suspended in the air. Then, the air passes through an outlet port, which is arranged in the post-filtering chamber, and enters combustion chambers of the internal combustion engine. In this manner, purified air from which foreign particles have been removed by the filter is drawn into the combustion chambers. This prevents problems such as foreign particles from being caught by engine pistons.
As such an air cleaner, a planar filter, which includes a plurality of parallel folds, is often used. In such an air cleaner, when the air in the pre-filtering chamber enters the post-filtering chamber through the filter, the air must be dispersed throughout the entire filtering surface of the filter. Otherwise, most of the air may pass through a particular portion of the filter. In such a case, most of the foreign particles are captured in only the particular portion of the filter. Accordingly, the filtering capacity of the filter cannot be used to its full extent. Further, the pressure loss of the air increases as it passes through the filter.
To solve these problems, for example, the distance between the inlet port and the filter, that is, the volume of the pre-filtering chamber, may be increased as much as possible. This would sufficiently disperse the air in the pre-filtering chamber before the air passes through the filter. Accordingly, the air passes throughout the entire filtering surface of the filter thereby allowing the filtering capacity of the filter to be used to its full extent.
However, such a structure would add limitations to the shapes and layout of the air cleaner and conduits, which are located upstream relative to the air cleaner. Therefore, there may be cases in which there is no way to avoid shortening of the distance between the inlet port and filter. In such cases, an increase in the pressure loss and decrease in the filtering capacity cannot be avoided.
The air cleaner discussed above is used in an intake system for an internal combustion engine. However, the afore-mentioned problems are not unique to air cleaners and may also occur in other types of gas filtering apparatuses.
Patent Publication 1: Japanese Examined Patent Publication No. 7-54109